This application claims the benefit of Korean Patent Application No. 2001-62936 filed on Oct. 12, 2001, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an illumination system and a projector adopting the same, and more particularly, to an illumination system which realizes a color image without a color wheel, and a projector adopting the illumination system.
2. Description of the Related Art
FIG. 1 shows a conventional projector comprising a light source 100, a first relay lens 102 which condenses a light beam emitted from the light source 100, a color wheel 105 which splits an incident light beam into R, G and B color light beams, a fly eye lens 107 which makes the light beam passing through the color wheel 105 uniform, a second relay lens 110 which condenses the light beam passing through the fly eye lens 107, a display device 112 which forms a color image from the R, G and B color light beams sequentially input through the color wheel 105, and a projection lens system 115 which magnifies and projects an image formed by the display device 112 toward a screen 118.
Generally, a xenon lamp, a metal-halide lamp, or a UHP lamp is used as the light source 100. These lamps unnecessarily emit a large amount of an infrared ray and an ultraviolet ray. Accordingly, as a lot of heat is generated, a cooling fan is necessarily used to drive the heat down. However, the cooling fan is one of sources that generates noise. In addition, since the spectrum of the lamp light source 100 is widely distributed across the entire wavelengths, due to a narrow color gamut, a selection of color is limited, a color purity is inferior, and the life span is short, so that a stable use of the lamp light source 100 is not possible.
In the conventional projector, to realize a color image, the color wheel 105 is rotated by a driving motor (not shown) at a high speed so as to sequentially illuminate the R, G and B color light beams onto the display device 112. R, G and B color filters (not shown) are equally arranged on the entire surface of the color wheel 105. Where three colors are sequentially used one by one during a rotation of the color wheel 105 according to a response speed of the display device 112, ⅔ of the light are lost. Additionally, since a gap is formed between neighboring color filters, for a preferable generation of a color, loss of light occurs at the gap.
Since the color wheel 105 rotates at a high speed, noise from the rotation of the color wheel 105 is also generated. Also, the mechanical movement of the driving motor has an ill effect on stability of the color wheel 105. In addition, due to a mechanical limit in the driving motor, it is difficult to obtain a speed over a certain degree, and a color breakup phenomenon occurs. Furthermore, since a unit price of the color wheel 105 is very high, the manufacturing cost of the projection is also high.
Accordingly, it is an object of the present invention to provide an illumination system which forms a color image without a color wheel by using a light emitting device that emits a light beam having a predetermined wavelength so as to improve the color purity and color gamut, and a projector adopting the illumination system.
It is another object of the present invention to provide an illumination system having at least one holographic optical element or a diffraction optical device which minimizes a cross section of a light beam so as to reduce a loss and volume of light, and a projector adopting the illumination system.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
To achieve the above and other objects of the present invention, there is provided an illumination system comprising an illumination unit including at least one light emitting device which emits a light beam having a predetermined wavelength and at least one holographic optical element which reduces a cross section of the light beam emitted from the light emitting device, and an optical path changer which changes a proceeding path of an incident light passing through the holographic optical element.
The light emitting device may be a light emitting device having an array structure.
The light emitting device may be one of a light emitting diode (LED), a laser diode (LD), an organic electro luminescent (EL), and a field emission display (FED).
The at least one holographic optical element may comprise a first holographic optical element which changes a proceeding direction of the light beam emitted from the light emitting device, and a second holographic optical element which reduces a diffraction angle of an incident light beam of which the proceeding direction is changed by the first holographic optical element. The at least one holographic optical element reduces a cross section of an incident light beam where the light beam is reflected by the optical path changer.
The first holographic optical element allows an incident light beam to be incident on the second holographic optical element at a predetermined angle of inclination and to be a parallel light beam.
The optical path changer may be a reflection minor.
The optical path changer may comprise a first optical path changer which changes the proceeding path of the incident light passing through the holographic optical element, and a second optical path changer which changes a proceeding path of the light beam passing through the first optical path changer by selectively transmitting or reflecting the light beam.
The at least one illumination unit may comprise a plurality of illumination units which emit light beams having different wavelengths, and are arranged in a line in a horizontal direction.
The second optical path changer may be a dichroic filter which filters or transmits a light beam passing through the first optical path changer according to a wavelength thereof.
The second optical path changer may be a cholesteric band modulation filter which reflects or transmits the light beam passing through the first optical path changer according to a polarization direction and a wavelength thereof.
The cholesteric band modulation filter may comprise a first mirror surface which reflects a light beam of a right circular polarization and transmits a light beam of a left circular polarization, with respect to a beam light having a predetermined wavelength, and a second mirror surface which transmits the light beam of the right circular polarization and reflects the light beam of the left circular polarization, with respect to the beam light having the predetermined wavelength.
The plurality of illumination units which emit light beams having different wavelengths can be arranged to be separated from one another at a predetermined angle.
The second optical path changer may be one of an X prism and an X type dichroic filter.
The illumination units may further be arranged in a multi-layer structure.
The illumination system having the plurality of light illumination units may further comprise a parallel light beam forming unit which produces a light beam emitted from a corresponding light emitting device or light emitting device array into a parallel light beam.
To achieve the above and other objects of the present invention, there is also provided an illumination system comprising at least one light emitting device or light emitting device array which emits a light beam having a wavelength, a first holographic optical element which condenses the light beam emitted from the light emitting device or light emitting device array, a second holographic optical element which produces an incident light beam passing through the first holographic optical element into a parallel light beam with a reduced cross section thereof, a third holographic optical element which reduces a diffraction angle of an incident light beam which is made into the parallel light beam by the second holographic optical element, and an optical path changer which changes a proceeding path of an incident light beam passing through the third holographic optical element.
The illumination system may comprise a plurality of light emitting devices or light emitting device arrays, wherein a third holographic optical element of a corresponding one of the light emitting devices or light emitting device arrays is disposed on a plane different from a plane of a neighboring third holographic optical element and does not prevent a proceeding path of a light beam from the neighboring third holographic optical element.
To achieve the above and other objects of the present invention, there is further provided an illumination system comprising at least one illumination unit having at least one light emitting device which emits a light beam having a predetermined wavelength and at least one diffractive optical device which reduces a cross section of the light beam emitted from the light emitting device, and an optical path changer which changes a proceeding path of an incident light beam input through the diffractive optical device.
To achieve the above and other objects of the present invention, there is provided a projector comprising at least one illumination unit including at least one light emitting device which emits a light beam having a predetermined wavelength and at least one holographic optical element which reduces a cross section of the light beam emitted from the light emitting device, an optical path changer which changes a proceeding path of an incident light input through the holographic optical element, a display device which processes an image signal of a light beam input from the optical path changer and forms an image thereof, and a projection lens unit which magnifies the image formed by the display device and projects the magnified image.